Magnetic recording devices, such as hard disk drives, are popularly used for the storage and retrieval of digital data because of their high capacity, low cost, and random access capability. In a hard disk drive, the digital data received from a computer is processed, encoded, and then written onto a circular, rigid disk. This disk is spun about a spindle by a spindle motor. As the disk is spun, the drive's servomechanism positions a transducer across the surface of the disk. Hence, the digital data is stored magnetically in a number of concentric circles, known as "tracks". Often, a number of disks are stacked together and accessed by a plurality of transducers. The same transducer can be used to both write data to the disk as well as read the data from the disk.
Whenever the computer is initially turned on, the spindle motor is "spun-up" (i.e., the spindle motor starts rotating the disk). The spinning disk creates a cushion of air, upon which the transducer can "fly" across the surface of a disk when moved from a starting track to a destination track (i.e., a "seek"). Usually, the spinning of the disk is maintained as long as the computer is turned on. However, disk drives for laptop and notebook computers are typically shut down after a period of non-use, in order to conserve power. When the disk drive is next accessed, the spindle motor is then spun-up.
Typically, the spindle motor is comprised of a three-phase motor. One problem inherent with three-phase motors is that of alignment. A three-phase motor is comprised of a rotating electromagnet and a permanent, stationary magnet. These magnets should be electrically and mechanically aligned. Otherwise, if these magnets were not properly aligned, the maximum torque would not be achieved. Indeed, improper alignment might even result in the spindle motor spinning backwards. Furthermore, there is a possibility that when current is first applied, the three-phase motor is near an unstable null torque position and, therefore, might not be able to move. This problem is exacerbated by the presence of friction.
In the prior art, these start-up problems inherent to three-phase motors were handled by using Hall effect devices to provide positional feedback information. And depending on the sensed information, the correct commutation state can then be activated. Three Hall effect devices were required-one for each of the three phases. The problems associated with adapting these Hall effect devices to spindle motor applications were cost, reliability, and size. These devices are quite costly and are subject to failures. Moreover, incorporating these devices consume a lot of printed circuit board space (which is critical for laptop, notebook, and hand-held computer systems). Another approach involved the use of separate, dedicated hardware to perform the start-up functions. Again, incorporating additional components was not cost effective, was subject to breakage, and wasted valuable space.
Thus, there is a need in the prior art for a fast, efficient, reliable, and inexpensive spindle start-up process. It would be preferable if such a process could be implemented without requiring additional hardware.